I got a friend of mine to make me some "sleeves" from the material that wicks moisture away and dries fast.. Forget what they call it, but, Under Armor makes some great Tees out of it. The sleeves look like the old time "Dealer Sleeves". Elastic at the top and bottom. The top hits me just below my pits and just above the Bicep. The bottom hits me at the wrist.I had them made from white material to reflect the sun. What I like about them is I don't burn with them and they feel cooler than a jacket, especially if you get them a little wet. Two other things I like. When you stop to eat you can just slip them off and cool off while eating, and at night you can rinse them out with soap and water in the sink and they dry in about an hour.
On really hot days, I recently purchased an HD vest you soak for about ten minutes and it keeps your core cool for several hours. I wear the sleeves with this too. I store it in a gallon zip lock bag, when it gets hot I fill the bag with water, let it sit, pull the vest out and save the remaining water for the next soak. Doesn't take up much room and works pretty well. Since I wear it over an Under Armor quick drying tee, I don't ever get that clammy feeling.